In a historic moment on Tuesday night, iconic New York Yankees relief pitcher and five-time World Series winner Mariano Rivera became the first-ever major league baseball player to get unanimously elected into the Hall of Fame.

Getting selected requires that at least 75 percent of the 425-person electorate vote for you. Rivera captured 425 out of 425 votes.

There's good reason: He's the greatest reliever in the history of the game, with a record 652 saves. In the playoffs, when pressure was on full-tilt, Rivera somehow got even better, with a 0.70 ERA over 141 innings and 42 postseason saves.

Those are ludicrous results for a man with an equally ridiculous set of tools. His four-seam fastball was filthy. Same for his two-seamer. His cutter was called "the single best pitch ever in the game" by fellow Hall of Famer Jim Thome.

He had an astounding understanding of "situational baseball"--who to pitch what in what situations. And yet, not even this was the biggest factor to Rivera's success. No, not even his baseball IQ.

It was his EQ.

Rivera's emotional intelligence was constantly on display, in terms of how he approached the game. And he was revered by his contemporaries for this skill, too.

Rivera's secret weapon: emotional intelligence

ESPN's Buster Olney got to know Rivera during his four-year tenure covering the Yankees for the New York Times. In Olney's recent words, Rivera believed:

"You should keep your emotions locked down in success or failure. When you won, you should act like it was the expected result, and if you lost, you should never, ever allow an opponent to think they had accomplished more than just winning that day's game."

That constant emotional tenacity allowed Rivera to keep his inner ferocious competitor fueled while displaying the cool demeanor of a detached observer on the outside. Sure, he'd get emotional--like everyone does--but it was always in response to his own shortcomings, never to a teammate's.

Olney tells the story of the first of only two home runs Rivera ever gave up in postseason history. Every entrepreneur should pay attention right now--it's about Rivera's uncanny ability to internalize failure in ways that kept him mentally prepared for whatever came next.

The home run came off the bat of Sandy Alomar Jr. I chose the words in that sentence very intentionally, as you'll see in a moment. The ball barely cleared the fence, just over the outstretched arm of outfielder Paul O'Neill, who slammed his glove to the field in frustration at having missed it.

Later, someone asked Rivera if Alomar's home run bothered him. Rivera responded, through gritted teeth, "No, because I made that homerun." Alomar didn't swing that hard, Rivera reasoned--so it only could have been the speed of the pitch that generated the home run.

Despite the unintended outcome, Rivera felt like he controlled the moment, not Alomar. Thus, he wasn't bothered.

Olney wrote this of Rivera's explanation: "I walked away awed by his instinctive mental gymnastics that so easily somersaulted him to a place of emotional comfort."

An EQ lesson for entrepreneurs

In business (and in life), you have weapons like wit, business savvy, and ambition at your disposal. Your greatest tool--and many a great, accomplished leader will tell you this--just might be emotional intelligence.

Rivera hurled a particularly potent form of emotional intelligence. He stayed calm under pressure. Especially under pressure.

How do you emulate that? Act like you've been there. Present yourself with grace and have respect for others, always. Blame only yourself. Understand that life is 10 percent what happens to you and 90 percent how you react to it, or choose to view it.

Here's another 90/10 realization. A good 90 percent of Rivera's Hall of Fame votes were surely due to his status as the greatest relief pitcher of all time. But there are plenty of other baseball legends in the Hall of Fame, and none of them were voted in unanimously.

Why was Rivera the first? My guess: The other 10 percent came from how he carried himself off the field, with his evolved EQ.

And that's something we all can bring to our own fields of play.